There are two general types of control systems for ventilators, or ventilation, known in the art. A first type of ventilation control system delivers gas to a patient based on a frequency that is selected by the clinician and is independent of patient activity. This type of ventilation, known as “controlled mechanical ventilation,” (CMV) is used when a patient needs a ventilator to breathe for him or her. Non-limiting examples of when a patient needs CMV include when the patient is non-alert, sedated, unresponsive, or paralyzed. A second type of ventilation control system, delivers gas to a patient in response to an inspiratory effort generated by the patient. This type of ventilation, which includes “assisted ventilation” or “augmented ventilation” and may be referred to as “respiratory support”, assists the patient to breathe. Non-limiting examples of patients who need or can benefit from this type of ventilation include patients suffering from respiratory insufficiency, respiratory impairment, or breathing disorders, such as patients suffering from COPD, pulmonary fibrosis, acute respiratory distress syndrome (ARDS), neuromuscular impairment, or sleep apnea. There are also ventilators and modes of ventilation that combine the two types of ventilators described above.
All ventilators comprise a ventilation interface connecting the ventilator to the patient. These interfaces can be non-invasive or invasive. A non-limiting example of non-invasive interfaces includes a mask over the nose and/or mouth. Non-limiting examples of invasive interfaces include an endotracheal tube, a tracheostomy tube, and a transtracheal catheter, which is placed into the airway of the patient.
A number of problems can arise during ventilation. The present invention addresses the problem of physical obstruction of inspiratory or expiratory airflow, which is one problem that can arise during ventilation. In the case of mechanical ventilation, an obstruction can occur anywhere in the gas delivery circuit or breathing circuit. Typically, such an obstruction in a mechanical ventilation system is annunciated by alarms, and an attending clinician is required to correct the problem, since the patient may not be capable of doing so. In the case of respiratory support ventilation, the obstruction can occur anywhere in the gas delivery circuit or breathing circuit, as well. In the case of respiratory support ventilation, there needs to be a valve somewhere in the gas delivery circuit or breathing circuit that can open or be opened to atmosphere so that the patient can breathe ambient air through that valve to prevent suffocation. Further, if the obstruction creates an overpressure condition, the same valve or a different valve must activate or be activated to open the gas delivery circuit to atmosphere to allow the lung pressure to decrease to prevent lung barotrauma.
In a more specific type of respiratory support ventilation, the patient receives gas from the ventilator in a gas delivery circuit known as an “open” system, meaning that the patient's lungs are open to atmosphere through their normal upper airway breathing routes (trachea, mouth, and nose). In this case, referred to throughout this specification as “open ventilation,” the patient is breathing “spontaneously,” or naturally, through their upper airway, but their breathing is augmented by receiving additional gas from the ventilator through the “open” gas delivery circuit. Typically the patient exhales directly to ambient through their airway and not through the gas delivery circuit. However, in some systems or some situations, that the patient may exhale through the gas delivery circuit. An open ventilation system is described in detail in US Patent Application No. 2005/003472 (Freitag) and in US Patent Application No. 2005/0005936 (Wondka), each of which is hereby incorporated by reference herein in its entirety. The ventilation interface in an open system is typically a transtracheal catheter that is placed percutaneously through the patient's neck into the tracheal lumen. Alternatively, the ventilation catheter is placed into an un-cuffed tracheostomy tube, a tracheostomy tube with a deflated cuff, a stent or stoma guide, such as a Montgomery T-Tube, or an airway prosthesis such as that shown in US Patent Application No. 2005/003472 (Freitag).
In “open” system ventilation, one concern about obstruction is an obstruction of the upper airway. Non-limiting examples of obstruction of the upper airway that may occur include swelling of the oro-pharyngeal structures; closure of the oro-pharyngeal structures, such as that which could occur in obstructive sleep apnea syndrome; stenosis of the airway caused, for example, by tracheal malacia; rapid swelling of the airway tissues; or inadvertent inflation of a cuff on a tracheostomy tube. If any event such these, or other airway-obstructing event, occurs, the patient is obstructed or restricted from being able to spontaneously breathe, and the amount of gas received from the ventilator through the open gas delivery circuit may not be enough to sustain respiration. Hence, an inspiratory and expiratory pressure or airflow relief mechanism is warranted in these circumstances to provide an additional spontaneous breathing route for the patient. The combination of labeling and an alert patient may obviate any real safety concern; however, providing a relief mechanism may provide some significant benefit and convenience to the users, and significantly improve efficacy of the therapy, or may be a significant benefit during product misuse, or during unanticipated clinical events.